Drilling assembly and method for drilling a barehole into geological formations

Abstract

A drilling assembly for drilling a borehole into geological formations. The assembly comprises a drilling shaft and a pump device, both placable in the borehole. The drilling shaft comprises a drilling head, and the pump device comprises a sealing device for sealing a first borehole part below the sealing device from a second borehole part above the sealing device. The pump device is enabled to pump a fluid from the first borehole part to the second borehole part.

1. A drilling assembly for drilling a borehole into geological formations, said drilling assembly comprising:
 a drilling shaft placable in the borehole, which shaft comprises a drilling head; 
 a pump device placable in the borehole, wherein the pump device comprises primary sealing means for sealing a first borehole part below the primary sealing means from a second borehole part above the primary sealing means, and wherein the pump device is enabled to pump a fluid from the first borehole part to the second borehole part; 
 a substantially tube shaped casing placable in the borehole, said casing comprising near one end of the casing a secondary sealing means for closing said one end of the casing whereby the first borehole part is divided into lower and upper sections, which secondary sealing means is capable of keeping the pressure in the lower section lower than the pressure in the upper section. 
 
     
     
       2. The drilling assembly of  claim 1 , wherein the secondary sealing means comprises a valve. 
     
     
       3. The drilling assembly of  claim 1 , wherein and wherein the primary sealing means includes a first sealing for sealing the pump device on the casing inner wall and a second sealing for sealing the pump device on the drilling shaft, such that in longitudinal direction the first borehole part is sealed off from the second borehole part. 
     
     
       4. The drilling assembly of  claim 1 , wherein the drilling shaft extends through the pump device, and the drilling shaft is rotatably arranged relative to the pump device. 
     
     
       5. The drilling assembly of  claim 1 , wherein the drilling shaft comprises a slick drilling string. 
     
     
       6. The drilling assembly of  claim 1 , wherein the pump device is drivable by a driving fluid or an electric motor. 
     
     
       7. The drilling assembly of  claim 1 , wherein the pump is retrievable from the borehole. 
     
     
       8. The drilling assembly of  claim 1 , wherein the one end of the casing corresponds to the bottom end of the casing when placed in the borehole. 
     
     
       9. A drilling assembly for drilling a borehole into geological formations, said drilling assembly comprising:
 a drilling shaft placable in the borehole, which shaft comprises a drilling head; 
 a pump device placable in the borehole, wherein the pump device comprises primary sealing means for sealing a first borehole part below the primary sealing means from a second borehole part above the primary sealing means, and wherein the pump device is enabled to pump a fluid from the first borehole part to the second borehole part; 
 
       a substantially tube shaped casing placable in the borehole, said casing comprising near one end of the casing a secondary sealing means for closing said one end of the casing, wherein an opening is arranged in the casing wall to which the pump device is connectable. 
     
     
       10. The drilling assembly of  claim 9 , wherein an annular space is defined between the casing and the borehole in which the casing is placed. 
     
     
       11. The drilling assembly of  claim 10 , wherein said annular space is defined between the casing and another casing fixedly arranged in the borehole. 
     
     
       12. The drilling assembly of  claim 10 , wherein means is provided for feeding a driving fluid through said annular space to the opening in the casing wall in order to drive the pump device. 
     
     
       13. The drilling assembly of  claim 9 , wherein the pump device is drivable by a driving fluid or an electric motor. 
     
     
       14. The drilling assembly of  claim 9 , wherein the secondary sealing means divides the first borehole part into lower and upper sections, and wherein the secondary sealing means is capable of keeping the pressure in the lower section lower than the pressure in the upper section. 
     
     
       15. A method of drilling a borehole into geological formations, the borehole comprising a secondary sealing means shutting off a bottom part of the borehole, said method comprising the following steps:
 arranging a drilling shaft in the borehole above the secondary sealing means, which shaft comprises a drilling head; 
 arranging a pump device in the borehole above the secondary sealing means, wherein the pump device comprises primary sealing means for sealing a first borehole part below the primary sealing means from a second borehole part above the primary sealing means, the drilling head being located in the first borehole part; 
 operating the pump device so as to reduce a hydrostatic pressure in the first borehole part; 
 opening the secondary sealing means; 
 driving the drill shaft to deepen the borehole below the secondary sealing means. 
 
     
     
       16. The method of drilling a borehole into geological formations of  claim 15 , wherein operating the pump device comprises pumping a fluid from the first borehole part to the second borehole part. 
     
     
       17. The method of drilling a borehole into geological formations of  claim 15 , further comprising:
 lifting the drilling shaft to a position in which the drilling head is located above the secondary sealing means; 
 closing the secondary sealing means. 
 
     
     
       18. The method of drilling a borehole into geological formations of  claim 17 , further comprising:
 allowing a subsequent increase in the hydrostatic pressure in the first borehole part. 
 
     
     
       19. The method of drilling a borehole into geological formations of  claim 18 , further comprising:
 removing the pump device from the borehole.